1. Field of the Invention
The present invention relates to an image forming optical system, particularly a decentering optical system having power at a reflecting surface for an optical apparatus, such as a video camera, a digital still camera, a film scanner, an endoscope, etc., in which a small imaging element is used, a holding structure of the decentering optical system and an optical apparatus using the same.
2. Description of the Related Art
Recently, in an image forming optical system for a video camera, a digital still camera, a film scanner, an endoscope, etc., achieving small sizing, weight lightening and low cost as for the optical system itself have been demanded with development of the miniaturization of the imaging element.
Conventionally, a prism optical systems using a free curved surface, etc. has been proposed for further thinning the optical system.
In an example, a state of positioning two prisms without having a rotationally asymmetric surface has been disclosed. Here, a depressed portion and a projected portion are formed as a position keeping means outside a light effective area on two faced surfaces of two prisms.
Furthermore, such composition has been disclosed that attaching of prisms is made while positioning of each prism is performed by fitting into the depressed portion and the projected portion.
In another example, a state of positioning of a prism having a rotationally asymmetric surface has been disclosed. Here, the depressed portion or the projected portion is formed in the prism.
With such disclosure, it has been also disclosed that a composition of positioning and fixing prisms on a holding component by forming a projected portion or a depressed portion which is fitted into the depressed portion or the projected portion of the prisms.
In other example, a state of positioning a prism having a rotationally asymmetric surface has been disclosed. Here, two projected portions are formed at a side surface of a prism, and a plane portion having two holes at a side surface of the other prism, each of which is fitted into the projected portion is formed. A composition for positioning and fixing two prisms by fitting these projected portions into the plane portion having holes has been disclosed. Furthermore, it has been also disclosed that a plane portion having holes formed at a side surface of the two prisms respectively, and a composition for positioning and fixing these prisms by using a screw from both sides of a rod-like component.